U.S. patent number 5,122,728 [Application Number 07/633,835] was granted by the patent office on 1992-06-16 for coupled inductor type dc to dc converter with single magnetic component.
This patent grant is currently assigned to Hughes Aircraft Company. Invention is credited to Christopher R. Ashley.
United States Patent |
5,122,728 |
Ashley |
June 16, 1992 |
Coupled inductor type DC to DC converter with single magnetic
component
Abstract
A coupled inductor type boost DC to DC converter with a single
multipurpose magnetic component. The invention includes a
conventional switch for converting an input DC voltage to a signal
having a time varying waveform. The switch Q1 has a pole terminal
connected to a source of input voltage, a control terminal and
first and second throw terminals. The single inductive element
includes a first winding LN.sub.1 connected between an output
terminal of the switch and an input terminal of the converter and a
second winding LN.sub.2 connected between the second throw terminal
of the switch and an output terminal of the converter. In a first
embodiment, the invention further includes a winding LN.sub.3 of
the inductive element connected at a first end to the control
terminal of the switch which provides a level shifting circuit for
shifting the level of a drive signal applied to the control
terminal of the switch.
Inventors: |
Ashley; Christopher R. (Redondo
Beach, CA) |
Assignee: |
Hughes Aircraft Company (Los
Angeles, CA)
|
Family
ID: |
24541315 |
Appl.
No.: |
07/633,835 |
Filed: |
December 26, 1990 |
Current U.S.
Class: |
323/282;
323/267 |
Current CPC
Class: |
H02M
3/33561 (20130101); H02M 3/005 (20130101); H02M
1/009 (20210501) |
Current International
Class: |
H02M
3/00 (20060101); H02M 3/24 (20060101); H02M
3/335 (20060101); G05F 001/577 () |
Field of
Search: |
;323/267,282,290,351,16
;363/124 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
White et al., "Two-Inductor Boost and Buck Converters", Jun. 1987,
Power Electronics Specialist Conference; pp. 387-392..
|
Primary Examiner: Sterrett; Jeffrey
Attorney, Agent or Firm: Lindeen, III; Gordon R. Mitchell;
Steven M. Denson-Low; Wanda K.
Claims
What is claimed is:
1. A coupled inductor type boost DC to DC converter comprising:
a switching element for converting an input DC voltage to a signal
having a time varying waveform, said switching element including a
switch having a control terminal and first and second throw
terminals; and
a first inductive element having:
a first winding connected between said first throw terminal of said
switch and an input terminal of said converter,
a second winding connected between said second throw terminal of
said switch and an output terminal of said converter, and
a third winding connected at a first end to said control terminal
of said switch, to thereby provide a level shifter for shifting the
level of a drive signal applied to said control terminal of said
switch.
2. The invention of claim 1 wherein said level shifter includes a
pulse width modulator circuit connected to a second end of said
third winding of said first inductive element.
3. The invention of claim 2 wherein said level shifter further
includes a driver connected in series between said pulse width
modulator circuit and said second end of said third winding of said
first inductive element.
4. The invention of claim 1 further including an auxiliary
regulated power supply circuit.
5. The invention of claim 4 wherein said auxiliary power supply
circuit includes a fourth winding of said first inductive element
connected at one end to a source of reference potential.
6. The invention of claim 5 wherein said auxiliary power supply
circuit includes a first diode connected at a first end to a second
end of said fourth winding of said first inductive element.
7. The invention of claim 6 wherein said auxiliary power supply
circuit includes a fifth winding of said first inductive element,
connected at a first end thereof to a second end of said first
diode.
8. The invention of claim 7 wherein said auxiliary power supply
circuit further includes a capacitor connected to said second end
of said first diode.
9. The invention of claim 8 wherein said auxiliary power supply
circuit further includes a second diode connected at a first end to
a second end of said fifth winding of said first inductive element
and at a second end to an output terminal of said auxiliary power
supply circuit.
10. The invention of claim 9 wherein said auxiliary power supply
circuit further includes a second capacitor connected between said
second end of said second diode and said source of reference
potential.
11. The invention of claim 1 further including a ripple
cancellation circuit including a fourth winding of said first
inductive element connected at a first end to said first throw
terminal of said switch and at a second end to a source of
reference potential.
12. The invention of claim 11 wherein said ripple cancellation
circuit further includes a second inductive element connected in
series with said fourth winding of said first inductive
element.
13. The invention of claim 12 wherein said ripple cancellation
circuit further includes a first capacitor connected in series with
said fourth winding of said first inductive element.
14. A coupled inductor type boost DC to DC converter
comprising:
a switching element for converting an input DC voltage to a signal
having a time varying waveform, said switching element including a
switch having a control terminal and first and second throw
terminals; and
a first inductive element having:
a first winding connected between said first throw terminal of said
switch and an input terminal of said converter,
a second winding connected between said second throw terminal of
said switch and an output terminal of said converter; and
an auxiliary regulated power supply circuit including a third
winding of said first inductive element connected at one end to a
source of reference potential, a first diode connected at a first
end to a second end of said third winding of said first inductive
element, a fourth winding of said first inductive element,
connected at a first end thereof to a second end of said first
diode, a capacitor connected to said second end of said first
diode, and a second diode connected at a first end to a second end
of said fourth winding of said first inductive element and at a
second end to an output terminal of said auxiliary power supply
circuit.
15. The invention of claim 14 wherein said auxiliary power supply
circuit further includes a second capacitor connected between said
second end of said second diode and said source of reference
potential.
16. The invention of claim 14 further including a fifth winding
connected at a first end to said control terminal of said switch
for shifting the level of a drive signal applied to said control
terminal of said switch.
17. The invention of claim 14 further including a fifth winding of
said first inductive element connected at a first end to said first
throw terminal of said switch and at a second end to said source of
reference potential to thereby provide a ripple cancellation
circuit.
18. The invention of claim 17 further including a second inductive
element connected in series with said fifth winding of said first
inductive element.
19. The invention of claim 18 further including a first capacitor
connected in series with said fifth winding of said first inductive
element.
20. A coupled inductor type boost DC to DC converter
comprising:
a switching element for converting an input DC voltage to a signal
having a time varying waveform, said switching element including a
switch having a control terminal and first and second throw
terminals; and
a first inductive element having:
a first winding connected between said first throw terminal of said
switch and an input terminal of said converter,
a second winding connected between said second throw terminal of
said switch and an output terminal of said converter, and
a ripple cancellation circuit including a third winding of said
first inductive element connected at a first end to said first
throw terminal of said switch and at a second end to a source of
reference potential.
21. The invention of claim 20 wherein said ripple cancellation
circuit further includes a second inductive element connected in
series with said third winding of said first inductive element.
22. The invention of claim 21 wherein said ripple cancellation
circuit further includes a first capacitor connected in series with
said third winding of said first inductive element.
23. A coupled inductor type boost DC to DC converter
comprising:
a switching element for converting an input DC voltage to a signal
having a time varying waveform, said switching element including a
switch having a control terminal and first and second throw
terminals;
a first inductive element having:
a first winding connected between said first throw terminal of said
switch and an input terminal of said converter,
a second winding connected between said second throw terminal of
said switch and an output terminal of said converter.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power conversion circuits and
systems. More specifically, the present invention relates to DC to
DC converters.
While the present invention is described herein with reference to
illustrative embodiments for particular applications, it should be
understood that the invention is not limited thereto. Those having
ordinary skill in the art and access to the teachings provided
herein will recognize additional modifications, applications, and
embodiments within the scope thereof and additional fields in which
the present invention would be of significant utility.
2. Description of the Related Art
DC to DC converters are known in the art. DC to DC converters
function to efficiently change a DC voltage from one level to
another. This conversion is typically accomplished with switching
mode power transistors which convert an input DC voltage to an AC
square wave and then convert the AC square wave to a higher or
lower voltage amplitude via the turns ratio transformation of a
power transformer. The transformer output square wave is then
rectified and filtered to generate the new DC voltage level at
higher or lower voltage relative to a different ground reference
than the input DC voltage power level.
DC to DC converters are often used to provide regulated power for
electronic and electrical systems from a source of unregulated
power. A variety of DC to DC converters are known in the art
including buck, boost and buck-boost converters. See "Two-Inductor
Boost and Buck Converters" by J. L. White and W. J. Muldoon
published in the IEEE 18th Annual Power Electronics Specialists
Conference June 21-26, 1987.
Boost type DC to DC converters are particularly useful. Boost type
DC to DC converters convert an input direct current (DC) signal at
a first lower voltage to an output DC voltage at a second higher
voltage level.
Coupled inductor type boost DC to DC converters utilize an inductor
to provide DC level shifting. Coupled inductor type boost DC to DC
converters are widely used due to the inherent ripple current
reduction capability of the inductive component. However,
conventional coupled inductor type boost DC to DC converters
typically utilize at least three separate magnetic components for
providing the functions of energy storage, power switch drive,
input current ripple cancellation and regulated low voltage supply
generation. The weight, size and cost associated with multiple
magnetic components has tended to limit the desirability of
conventional coupled inductor type boost DC to DC converters for
certain applications, e.g. spacecraft power systems.
Thus, there is a need in the art for a small, light weight, low
cost improved coupled inductor type boost DC to DC converter design
capable of performing the functions of energy storage, power switch
drive, input current ripple cancellation and regulated low voltage
supply generation.
SUMMARY OF THE INVENTION
The need in the art is addressed by the present invention which
provides a coupled inductor type boost DC to DC converter with a
single multi-purpose magnetic component. The invention includes a
conventional switch for converting an input DC voltage to a signal
having a time varying waveform. The switch Q1 has a pole terminal
connected to a source of input voltage, a control terminal and
first and second throw terminals. The single inductive element
includes a first winding LN.sub.1 connected between an output
terminal of the switch and an input terminal of the converter and a
second winding LN.sub.2 connected between the second throw terminal
of the switch and an output terminal of the converter.
In a first embodiment, the invention further includes a winding
LN.sub.3 of the inductive element connected at a first end to the
control terminal of the switch which provides a level shifting
circuit for shifting the level of a drive signal applied to the
control terminal of the switch.
In a second embodiment, the invention includes a winding LN.sub.4
of the first inductive element connected at a first end to the
first throw terminal of the switch Q1 and at a second end to a
source of reference potential to thereby provide an input current
ripple cancellation circuit.
In a third embodiment, the invention includes an auxiliary
regulated power supply circuit including a winding LN.sub.5 of the
first inductive element connected at one end to the source of
reference potential, a first diode CR2 connected at a first end to
a second end of the winding LN.sub.5 of the first inductive
element, a winding LN.sub.6, of the first inductive element,
connected at a first end thereof to a second end of the first
diode, a capacitor C4 connected to the second end of the first
diode, and a second diode CR3 connected at a first end to a second
end of the winding LN.sub.6 of the first inductive element and at a
second end to an output terminal of the regulated auxiliary power
supply circuit.
Hence, the inductor coupled DC to DC converter of the present
invention provides conventional energy storage, power switch drive
level shifting, input current ripple cancellation, and regulated
low voltage auxiliary power supply generation with a single
magnetic component. The invention allows for a significant
reduction in parts count, unit size and cost over comparable prior
designs.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is an illustrative schematic diagram of a two inductor
boost converter.
FIG. 1(b), is an illustrative schematic diagram of a coupled
inductor buck converter.
FIG. 1(c), is an illustrative schematic diagram of a coupled
inductor Cuk converter.
FIG. 2 is a simplified schematic diagram of the coupled inductor
boost converter of the present invention.
FIG. 3 shows a schematic diagram of a preferred embodiment of the
coupled inductor boost converter of the present invention.
FIGS. 4(a) through 4(i) illustrate voltage and current waveforms in
the coupled inductor circuit of FIG. 3.
DESCRIPTION OF THE INVENTION
Illustrative embodiments and exemplary applications will now be
described with reference to the accompanying drawings to disclose
the advantageous teachings of the present invention.
The topology of the coupled inductor DC to DC converter of the
present invention is best illustrated with a review of the family
origins thereof. The topology in its most basic form is a two
(choke) inductor boost converter 10 with a single-pole-double-throw
switch S1 as shown in FIG. 1(a). The pole of the switch S1 is
connected to one terminal of an input voltage source V.sub.in. A
first throw terminal of the switch S1 is connected to one end of a
first inductor L1 while a second throw terminal is connected to one
end of a second inductor L2. A first capacitor C1 is connected
between the first and second throw terminals of the switch S1. An
output capacitor C2 is connected between the second terminals of
the first and second inductors L1 and L2. The switch S1 converts
the input DC voltage to an AC quasi-square wave. An output voltage
V.sub.out is developed across a load represented by a resistor
R.sub.load.
As shown in FIG. 1(b), if the terminals of the topology are rotated
one position clockwise, a coupled inductor buck converter 20 with
continuous input and output current is derived. If the basic power
stage terminals are rotated one position counter-clockwise, as
shown in FIG. 1(c), a "Cuk" converter 30 is derived.
Like the "Cuk" converter, the input and output currents of both
topologies are non-pulsating. Since L1 and L2 have essentially the
same AC voltage, a single coupled inductor can replace the two
individual inductors. Output ripple current is dramatically reduced
by the introduction of a small inductance in series with the output
leg of the coupled inductor.
FIG. 2 is a simplified schematic diagram of the coupled inductor
boost converter 40 of the present invention. A power MOSFET
transistor Q1 and a diode CR1 form the single-pole double-throw
switch. The main choke L1 has three windings. L1A and L1B are the
main coupled inductor power windings; L1C is an auxiliary winding
used to cancel input ripple current. C3 is the energy transfer
capacitor buried inside the topology. C2 is a DC blocking capacitor
for the input ripple cancellation circuit. C1 and C4 are the input
and output capacitors. L2 is the input ripple cancellation
inductor. L3 is the output ripple reduction choke.
This topology has the DC characteristics of a boost converter. If
the voltage across the output capacitor C4 is defined to be
V.sub.out, the voltage across the energy transfer capacitor C3 must
equal the V.sub.out in the steady state. During the "on" time, the
voltage across L1A (and therefore L1B) is equal to the input
voltage V.sub.in. During the "off" time, the voltage across L1A is
V.sub.in minus V.sub.out. Since the average voltage across the
inductor L1A must be zero,
where D is the duty cycle of the switch which varies from 0 to 1 as
controlled by the base drive to the transistor Q1 (not shown).
Solving for V.sub.out yields, the standard DC boost converter
transfer function:
Low output current ripple is achieved by the introduction of the
ripple reduction choke L3. L3 forces all of the L1 magnetizing
current to flow in winding L1B. If the energy transfer capacitor C3
is very large (i.e., no significant ripple voltage), the voltage
across C3 is equal and opposite to the voltage across the output
capacitor C4. Also, the voltage across L1A is equal and opposite to
the voltage across L1B. As a result, the voltage across L3 and the
ripple current in L3 approach zero and the output ripple voltage
approaches zero. The input ripple cancellation circuit uses a
current cancellation technique in which an AC current is injected
which is equal to but 180 degrees out-of-phase with the ripple
current flowing in L1. When the two currents are added together,
the net AC current approaches zero. The condition for zero ripple
is derived as follows from the differential equations for the
coupled inductor power stage during the "on" time (assuming a large
blocking capacitor, C2):
where L1=L1A=L1B, N.sub.1 and N.sub.2 are the number of turns on
the windings L1B and L1C respectively, of L1. Zero ripple occurs
when dL1/dt=dL2/dt. Therefore, given n N.sub.2 /N.sub.1 ; ##EQU1##
Solving for L2 as a function of L1 and n yields:
Typically, the turns ratio n will be on the order of 3 so that L2
will be only 0.2222.times.L1. Since the inductance of L2 is quite
small and it only carries the AC ripple current, L2 will be
significantly smaller than a conventional EMI filter choke designed
to carry the full DC input current of the converter.
FIG. 3 shows a schematic diagram of a preferred embodiment of the
coupled inductor boost converter 50 of the present invention. The
embodiment of FIG. 3 is a coupled-inductor boost DC to DC converter
topology which uses fixed frequency pulse-width modulation to
regulate output voltage at a constant value over a relatively wide
range of input voltage and output current. The embodiment of FIG. 3
is identical to that of FIG. 2 with the exception that the input
capacitor C1 is combined with the DC blocking capacitor C2 as a
single capacitor C1 in series with the inductor L1; the inductors
L1A and L3 are combined in a single winding LN.sub.2. Windings
LN.sub.1 and LN.sub.2 are DC inductors and perform the energy
storage function for the converter topology. Winding LN.sub.3
provides level shifting of the zero volt referenced drive signal in
order to control the state of the switch Q1 such that the voltage
waveform at terminal Q1-2 referenced from Q1-3 is the same as the
voltage at V.sub.drive relative to ground. Winding LN.sub.4 has a
reduced turns-ratio (i.e., N.sub.4 /N.sub.1 <1) allowing
selection of L2 (using equation [10] below). Windings LN.sub.5 and
LN.sub.6 are included to provide a regulated auxiliary low voltage
supply. The switch Q1 is a power MOSFET and requires a positive
voltage on pin 2 relative to pin 3 in order to turn on and is off
for a drive voltage of approximately zero volts. The same
configuration can be used to drive a current driver switch such as
a bipolar transistor.
In steady state operation, the inductors appear as shorts and the
capacitors appear as opens (assuming throughout that the resistance
of the windings is negligible). Thus, the input voltage V.sub.in
(typically 25-48 volts) is applied to the input capacitor C1. Since
in this boost configuration, the output voltage V.sub.out
(typically 50 volts) is higher than the input voltage V.sub.in, the
diode CR1 is back biased and off. With the switch Q1 off, the
voltage on C2 is equal to the voltage on C3. Then a drive voltage
(e.g., 15 volts) is applied to the base of the switching transistor
Q1 at pin 2 by a pulse width modulator circuit 52 via a driver 54.
The pulse width modulator 52 may be implemented with a UC1842 made
by Unitrobe Corp. in Lexington, Mass., while the driver 54 may be
implemented with a TSC4424 made by Teledyne Semiconductor Inc..
When the switch Q1 (a power MOSFET transistor) comes on, a short is
provided between pins 1 and 3. Thus, the voltage on pin 3 increases
to V.sub.in, e.g., 40 volts. At that point, the input voltage is
applied to pin 1 and across LN.sub.3. With say 15 volts at the
bottom of the inductor LN.sub.3 and 40 volts across LN.sub.3, a net
55 volts is applied to pin 2 of the transistor switch Q1, keeping
it on. The voltage at the top of the energy transfer capacitor C2
jumps from V.sub.in minus a diode drop e.g., 39.3 volts to V.sub.in
plus V.sub.out e.g., 90 volts. The ratio between the input voltage
and the output voltage is given from equation [2] as:
As the voltage rises across LN.sub.1, the current I.sub.1a in
LN.sub.1 rises. This induces a current in LN.sub.4 in the opposite
direction. By choosing the turns ratio in accordance with equation
[10] below, a cancellation of input ripple current may be
achieved.
where n=N.sub.1 /N.sub.4 where N.sub.1 is the number of turns in
the winding of the inductor LN.sub.1 and N.sub.4 is the number of
turns in the winding of the inductor LN.sub.4.
When the switch Q1 is on, the voltage v.sub.1 on LN.sub.1 appears
as v.sub.5 across LN.sub.5 in accordance with the turns ratio. This
voltage is applied to the capacitor C4 via a second diode CR2. When
the switch Q1 is off, the negative voltage V.sub.1 across LN.sub.1,
V.sub.in -V.sub.out, as determined by the turns ratio, is applied
to LN.sub.6 as v.sub.6. This voltage will add to the voltage across
C4 and the voltage across C5 minus the diode drop across CR3 and is
output as V.sub.o2. Thus, windings LN.sub.5 and LN.sub.6 detect the
peak-to-peak voltage across LN.sub.1 (which is the output voltage
V.sub.out). Since V.sub.out is regulated, these windings provide a
second regulated output voltage V.sub.o2 which is applied to the
pulse width modulator as a housekeeping supply, along with the
output voltage V.sub.out. Thus, neglecting rectifier voltage
drops:
V.sub.o2 =(N.sub.5 /N.sub.1)V.sub.in -N.sub.6 /N.sub.1 (V.sub.in
-V.sub.out)[11]
FIGS. 4(a) through 4(i) illustrate steady state voltage and current
waveforms in the coupled inductor circuit 50 of FIG. 3. With
N.sub.1 =N.sub.2 =N.sub.3, the voltage waveforms are all equal and
in-phase as shown.
Hence, the inductor coupled DC to DC converter of the present
invention provides conventional energy storage, power switch drive
level shifting, input current ripple cancellation, and regulated
low voltage auxiliary power supply generation with a single
magnetic component. The invention allows for a significant
reduction in parts count, unit size and cost over comparable prior
designs.
Thus, the present invention has been described herein with
reference to a particular embodiment for a particular application.
Those having ordinary skill in the art and access to the present
teachings will recognize additional modifications applications and
embodiments within the scope thereof. While the windings are shown
in the drawings as having ferrite cores, those having ordinary
skill in the art will recognize that other types of cores or
windings without cores of any kind may be used depending on the
characteristics desired for the windings for a particular
application.
It is therefore intended by the appended claims to cover any and
all such applications, modifications and embodiments within the
scope of the present invention.
Accordingly,
* * * * *